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Subject: Re: [PATCH] mmc: mmc: Fix HS setting in mmc_hs400_to_hs200()
From:   Chaotian Jing <chaotian.jing@mediatek.com>
To:     Adrian Hunter <adrian.hunter@intel.com>
CC:     Ulf Hansson <ulf.hansson@linaro.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Shawn Lin <shawn.lin@rock-chips.com>,
        "Simon Horman" <horms+renesas@verge.net.au>,
        Kyle Roeschley <kyle.roeschley@ni.com>,
        Hongjie Fang <hongjiefang@asrmicro.com>,
        "Harish Jenny K N" <harish_kandiga@mentor.com>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        <linux-mediatek@lists.infradead.org>,
        srv_heupstream <srv_heupstream@mediatek.com>
Date:   Wed, 13 Feb 2019 08:54:35 +0800
In-Reply-To: <566c0c11-be9c-73a3-d7ff-34aed3ad7db0@intel.com>
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On Tue, 2019-02-12 at 10:04 +0200, Adrian Hunter wrote:
> On 12/02/19 4:04 AM, Chaotian Jing wrote:
> > On Tue, 2019-02-05 at 15:42 +0200, Adrian Hunter wrote:
> >> On 5/02/19 3:06 PM, Ulf Hansson wrote:
> >>> On Mon, 4 Feb 2019 at 14:42, Adrian Hunter <adrian.hunter@intel.com> wrote:
> >>>>
> >>>> On 4/02/19 12:54 PM, Ulf Hansson wrote:
> >>>>> On Mon, 4 Feb 2019 at 10:58, Adrian Hunter <adrian.hunter@intel.com> wrote:
> >>>>>>
> >>>>>> On 1/02/19 10:10 AM, Ulf Hansson wrote:
> >>>>>>> On Fri, 1 Feb 2019 at 02:38, Chaotian Jing <chaotian.jing@mediatek.com> wrote:
> >>>>>>>>
> >>>>>>>> On Thu, 2019-01-31 at 16:58 +0100, Ulf Hansson wrote:
> >>>>>>>>> On Thu, 31 Jan 2019 at 08:53, Chaotian Jing <chaotian.jing@mediatek.com> wrote:
> >>>>>>>>>>
> >>>>>>>>>> mmc_hs400_to_hs200() begins with the card and host in HS400 mode.
> >>>>>>>>>> Therefore, any commands sent to the card should use HS400 timing.
> >>>>>>>>>> It is incorrect to reduce frequency to 50Mhz before sending the switch
> >>>>>>>>>> command, in this case, only reduce clock frequency to 50Mhz but without
> >>>>>>>>>> host timming change, host is still in hs400 mode but clock changed from
> >>>>>>>>>> 200Mhz to 50Mhz, which makes the tuning result unsuitable and cause
> >>>>>>>>>> the switch command gets response CRC error.
> >>>>>>>>>
> >>>>>>>>> According the eMMC spec there is no violation by decreasing the clock
> >>>>>>>>> frequency like this. We can use whatever value <=200MHz.
> >>>>>>>>>
> >>>>>>>>> However, perhaps in practice this becomes an issue, due to the tuning
> >>>>>>>>> for HS400 has been done on the "current" frequency.
> >>>>>>>>>
> >>>>>>>>> As as start, I think you need to clarify this in the changelog.
> >>>>>>>>>
> >>>>>>>> Yes, reduce clock frequency to 50Mhz is no Spec violation, but it may
> >>>>>>>> cause __mmc_switch() gets response CRC error, decreasing the clock but
> >>>>>>>> without HOST mode change, on the host side, host driver do not know
> >>>>>>>> what's operation the core layer want to do and can only set current bus
> >>>>>>>> clock to 50Mhz, without tuning parameter change, it has a chance lead to
> >>>>>>>> response CRC error. even lower clock frequency, but with the wrong
> >>>>>>>> tuning parameter setting(the setting is of hs400 tuning @200Mhz).
> >>>>>>>
> >>>>>>> Right, makes sense.
> >>>>>>>
> >>>>>>>>>>
> >>>>>>>>>> this patch refers to mmc_select_hs400(), make the reduce clock frequency
> >>>>>>>>>> after card timing change.
> >>>>>>>>>>
> >>>>>>>>>> Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
> >>>>>>>>>> ---
> >>>>>>>>>>  drivers/mmc/core/mmc.c | 8 ++++----
> >>>>>>>>>>  1 file changed, 4 insertions(+), 4 deletions(-)
> >>>>>>>>>>
> >>>>>>>>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> >>>>>>>>>> index da892a5..21b811e 100644
> >>>>>>>>>> --- a/drivers/mmc/core/mmc.c
> >>>>>>>>>> +++ b/drivers/mmc/core/mmc.c
> >>>>>>>>>> @@ -1239,10 +1239,6 @@ int mmc_hs400_to_hs200(struct mmc_card *card)
> >>>>>>>>>>         int err;
> >>>>>>>>>>         u8 val;
> >>>>>>>>>>
> >>>>>>>>>> -       /* Reduce frequency to HS */
> >>>>>>>>>> -       max_dtr = card->ext_csd.hs_max_dtr;
> >>>>>>>>>> -       mmc_set_clock(host, max_dtr);
> >>>>>>>>>> -
> >>>>>>>>>
> >>>>>>>>> As far as I can tell, the reason to why we change the clock frequency
> >>>>>>>>> *before* the call to __mmc_switch() below, is probably to try to be on
> >>>>>>>>> the safe side and conform to the spec.
> >>>>>>>>>
> >>>>>>>> Agree, it Must be more safe with lower clock frequency, but the
> >>>>>>>> precondition is to make the host side recognize current timing is not
> >>>>>>>> HS400 mode. it has no method to find a safe setting to ensure no
> >>>>>>>> response CRC error when reduce clock from 200Mhz to 50Mhz.
> >>>>>>>>> However, I think you have a point, as the call to __mmc_switch(),
> >>>>>>>>> passes the "send_status" parameter as false, no other command than the
> >>>>>>>>> CMD6 is sent to the card.
> >>>>>>>>>
> >>>>>>>> yes, the send status command was sent only after __mmc_switch() done.
> >>>>>>>>>>         /* Switch HS400 to HS DDR */
> >>>>>>>>>>         val = EXT_CSD_TIMING_HS;
> >>>>>>>>>>         err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING,
> >>>>>>>>>> @@ -1253,6 +1249,10 @@ int mmc_hs400_to_hs200(struct mmc_card *card)
> >>>>>>>>>>
> >>>>>>>>>>         mmc_set_timing(host, MMC_TIMING_MMC_DDR52);
> >>>>>>>>>>
> >>>>>>>>>> +       /* Reduce frequency to HS */
> >>>>>>>>>> +       max_dtr = card->ext_csd.hs_max_dtr;
> >>>>>>>>>> +       mmc_set_clock(host, max_dtr);
> >>>>>>>>>> +
> >>>>>>>>>
> >>>>>>>>> Perhaps it's even more correct to change the clock frequency before
> >>>>>>>>> the call to mmc_set_timing(host, MMC_TIMING_MMC_DDR52). Otherwise you
> >>>>>>>>> will be using the DDR52 timing in the controller, but with a too high
> >>>>>>>>> frequency.
> >>>>>>>>>
> >>>>>>>> for Our host, it has no impact to change the clock before or after
> >>>>>>>> change timing, as the mmc_set_timing() is only for host side, not
> >>>>>>>> related to MMC card side and no commands sent do card before the
> >>>>>>>> timing/clock change completed.
> >>>>>>>
> >>>>>>> Alright. After a second thought, it actually looks more consistent
> >>>>>>> with mmc_select_hs400() to do it after, as what you propose in
> >>>>>>> $subject patch.
> >>>>>>>
> >>>>>>> So, let's keep it as is.
> >>>>>>>
> >>>>>>>>>>         err = mmc_switch_status(card);
> >>>>>>>>>>         if (err)
> >>>>>>>>>>                 goto out_err;
> >>>>>>>>>> --
> >>>>>>>>>> 1.8.1.1.dirty
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Finally, it sounds like you are trying to fix a real problem, can you
> >>>>>>>>> please provide some more information what is happening when the
> >>>>>>>>> problem occurs at your side?
> >>>>>>>>>
> >>>>>>>> Yes, I got a problem with new kernel version. with
> >>>>>>>> commit:57da0c042f4af52614f4bd1a148155a299ae5cd8, this commit makes
> >>>>>>>> re-tuning every time when access RPMB partition.
> >>>>>>>
> >>>>>>> Okay, could you please add this as fixes tag for the next version of the patch.
> >>>>>>>
> > Ok, sorry for late reply due to Chinese New Year.
> >>>>>>>>
> >>>>>>>> in fact, our host tuning result of hs400 is very stable and almost never
> >>>>>>>> get response CRC error with clock frequency at 200Mhz. but cannot ensure
> >>>>>>>> this tuning result also suitable when running at HS400 mode @50Mhz. as I
> >>>>>>>> mentioned before, the host side does not know the reason of reduce clock
> >>>>>>>> frequency to 50Mhz at HS400 mode, so what's the host side can do is only
> >>>>>>>> reduce the bus clock to 50Mhz, even it can just only set the tuning
> >>>>>>>> setting to default when clock frequency lower than 50Mhz, but both card
> >>>>>>>> & host side are still at HS400 mode, still cannot ensure this setting is
> >>>>>>>> suitable.
> >>>>>>>
> >>>>>>> Right, thanks for clarifying.
> >>>>>>>
> >>>>>>> So I am expecting a new version with a fixes tag and some
> >>>>>>> clarification of the changelog, then I am ready to apply this to give
> >>>>>>> it some test.
> >>>>>>
> >>>>>> The switch from HS400 mode is done for tuning at times when CRC errors are a
> >>>>>> possibility e.g. after a CRC error during transfer.  So if the frequency is
> >>>>>> not to be reduced, then some mitigation is needed for the possibility that
> >>>>>> the CMD6 response itself will have a CRC error.
> >>>>>
> >>>>> That's a good point!
> >>>>>
> >>>>> However, how can we know that a CMD6 command is successfully
> >>>>> completed, if there is CRC errors detected during the transmission? I
> >>>>> guess we can't!?
> >>>>
> >>>> Yes, in that case, the only option is to assume the CMD6 was successful,
> >>>> like in
> >>>>
> >>>>   commit ef3d232245ab7a1bf361c52449e612e4c8b7c5ab
> >>>>   Author: Adrian Hunter <adrian.hunter@intel.com>
> >>>>   Date:   Fri Dec 2 13:16:35 2016 +0200
> >>>>
> >>>>       mmc: mmc: Relax checking for switch errors after HS200 switch
> >>>
> >>> Well, relaxing the check for switch errors, is to me a different
> >>> thing. This means we are first doing the CMD6, then allowing the
> >>> following status command (CMD13) to have CRC errors. Actually, even
> >>> the spec mention this as a case to consider. I guess it's because the
> >>> card internally have switched to a new speed mode timing.
> >>>
> >>> Allowing CRC errors for the actual CMD6 sound more fragile to me. Of
> >>> course, we can always try and see what happens.
> >>>
> >>> Chaotian, can you give it a go? Somehow, change the call to
> >>> __mmc_switch() in mmc_hs400_to_hs200(), so the CMD6 doesn't have the
> >>> CRC flag set.
> >>>
> > Yes, but should we add a new argument of __mmc_switch(), like "bool
> > ignore_crc" ?? for now, there are too many argument of __mmc_switch().
> 
> One solution for too many arguments is to make a structure to contain them. e.g.
> 
> struct mmc_switch_args {
> 	u8 set;
> 	u8 index;
> 	u8 value;
> 	unsigned int timeout_ms;
> 	unsigned char timing;
> 	bool use_busy_signal;
> 	bool send_status;
> 	bool retry_crc_err;
> };
> 
> int __mmc_switch(struct mmc_card *card, struct mmc_switch_args *args)
> 
Sure, I will upload new patch to do that.
> >>>>
> >>>> If we are going to do that, then we could stick with lowering the frequency
> >>>> first.
> >>>
> >>> Let's see what Chaotian's test may show.
> >>>
> >>>>
> >>>> Also I wonder if the mediatek driver could change to fixed sampling in
> >>>> ->set_ios() when the frequency drops for HS400 mode?
> >>>
> >>> Well, this sounds like a generic problem so if this is a possible
> >>> generic solution that would be great.
> >>>
> >>> Is this what sdhci is doing already?
> >>
> >> Not at present, but some drivers seem to be adjusting their settings for
> >> HS400 based on the frequency e.g. sdhci_msm_hs400()
> > 
> > It's hard to find a suitable setting for all cards when running at HS400
> > mode @50Mhz.
> > 
> > 
>